(1) Field of the Invention
This invention relates to finishing processes for textiles, and more particularly to the use of phosphonic acid derivatives as catalysts in the treatment of cellulose-containing materials with agents to give dimensional stability, durable press, and flame resistant textile products.
It is well known that dimensional stability, durable press, and flame resistance of cellulose-containing textiles can be enhanced by suitable treatment of such materials with certain chemical agents. The chemical agents employed in such treatments generally require catalysts to affect reaction with the cellulosic component to achieve improvement of the desirable properties in the finished products. Considerations of cost, efficiency, compatibility, toxicity, pollution effects, and many other factors have limited the scope of catalysts acceptable in finishing operations. Those catalysts widely employed in the processing of textiles for durable press, for instance, are not normally useful in other processes.
(2) Description of the Prior art
In the prior art we find reference to at least three finishing processes reportedly useful in producing products with improved dimensional stability, durable press performance, and flame resistance. These processes are mild cure, damp or moist cure, and pad-dry-cure finishing procedures. The latter process, and with modifications thereof, has been the most widely practiced commercially.
Mild cure and damp cure processes were developed as rather special techniques particularly to achieve high wet wrinkle resistance. These processes require catalysts that normally are not acceptable for use in other processes. In general, catalysts for these two processes were prepared by moderating mineral acids, as acids alone required very precise control of treatment conditions to avoid overcuring and severe strength loss.
Mild cure finishing is accomplished by padding fabric with a chemical agent to react with cellulose and strong catalyst, then heating the wet, impregnated fabric at about 60.degree.-100.degree. C for a short time without a pre-drying step. Detailed description of this process is given in the Textile Chemist and Colorist, Volume 1, page 415, 1969, and Volume 2, page 337, 1970.
Damp or moist cure finishing is similar to mild cure finishing in that a chemical agent and a strong catalyst are applied to fabric but then moisture content is carefully reduced to the range of 6-12%, after which fabric is sealed in a package to prevent moisture loss and held at room temperature for 12-24 hours, then neutralized and washed. More specific description of this process is given in U.S. Pat. No. 3,409,462.
Pad-dry-cure finishing follows the sequence of impregnating fabric with a chemical agent and catalyst, drying at a moderately elevated temperature, generally not exceeding about 100.degree. C, then curing at temperatures of 150.degree. to about 180.degree. C.
In the widely used pad-dry-cure process, Lewis acid type catalysts have been dominant in durable press finishing. Two salts, zinc nitrate and magnesium chloride, have been the principal catalysts used by industry.
A serious problem exists in the textile industry with the two catalysts most widely used in wrinkle resistant finishing, zinc nitrate and magnesium chloride. Several geographical areas have either banned or heavily restricted the use of zinc nitrate or any heavy-metal salt because plant effluents cause stream pollution. Also, many finishers have found that nitrate catalysts can cause shade changes with certain dyestuffs or yellowing on some white goods. Many textile plants can no longer use magnesium chloride or any halide-containing catalyst for fear of generation of bis(chloromethyl) ether which has been designated as carcinogenic. In addition, fuel and chemical shortages are causing finishers to seek catalysts that allow processing to be conducted with lower curing temperatues and faster curing times in an effort to conserve energy.
Traditionally, chemical finishing treatments to produce flame resistance also have been carried out by the pad-dry-cure process. Catalyst systems usually consist of some type of Lewis acid or combination of a Lewis acid and an organic acid but there are no outstanding catalysts that dominate this field. Sanderson et al, Textile Research Journal 40, pages 217-222 (1970) have employed lower dialkyl and trialkyl phosphites as phosphonate precursors to become a substantial part of the ultimate flame resistant product but these phosphites are reactive agents and not catalysts. Wedell, U.S. Pat. No. 2,953,481, teaches the use as catalysts of high-molecular phosphonic acid salts that are derived from low-molecular aliphatic amines, diamines, oxyalkylamines, etc. which are volatile or readily react with formaldehyde. However, only phosphonic acids of at least 8 carbon atoms are operative in the Wedell disclosure. Sommer et al, U.S. Pat. No. 3,219,407, describe the use of copolymers of vinyl phosphonic acid of 50-100 molecular units as catalysts in creaseproofing cellulose textiles and claim improved strength in the finished product. Monomeric, saturated phosphonic acids were not so employed.
While the treatments and processes described above impart highly desirable properties to cellulose-containing textiles, there are a multitude of catalysts required, and no one specific class is satisfactory in all cases.